Datasheet

© 2006 Microchip Technology Inc. DS70117F-page 31
dsPIC30F6011/6012/6013/6014
3.2 Data Address Space
The core has two data spaces. The data spaces can be
considered either separate (for some DSP instruc-
tions), or as one unified linear address range (for MCU
instructions). The data spaces are accessed using two
Address Generation Units (AGUs) and separate data
paths.
3.2.1 DATA SPACE MEMORY MAP
The data space memory is split into two blocks, X and
Y data space. A key element of this architecture is that
Y space is a subset of X space, and is fully contained
within X space. In order to provide an apparent linear
addressing space, X and Y spaces have contiguous
addresses.
When executing any instruction other than one of the
MAC class of instructions, the X block consists of the 64-
Kbyte data address space (including all Y addresses).
When executing one of the MAC class of instructions,
the X block consists of the 64-Kbyte data address
space excluding the Y address block (for data reads
only). In other words, all other instructions regard the
entire data memory as one composite address space.
The MAC class instructions extract the Y address space
from data space and address it using EAs sourced from
W10 and W11. The remaining X data space is
addressed using W8 and W9. Both address spaces are
concurrently accessed only with the MAC class
instructions.
The data space memory maps are shown in Figure 3-8
and Figure 3-9.
3.2.2 DATA SPACES
The X data space is used by all instructions and sup-
ports all addressing modes. There are separate read
and write data buses. The X read data bus is the return
data path for all instructions that view data space as
combined X and Y address space. It is also the X
address space data path for the dual operand read
instructions (MAC class). The X write data bus is the
only write path to data space for all instructions.
The X data space also supports Modulo Addressing for
all instructions, subject to addressing mode restric-
tions. Bit-Reversed Addressing is only supported for
writes to X data space.
The Y data space is used in concert with the X data
space by the MAC class of instructions (CLR, ED,
EDAC, MAC, MOVSAC, MPY, MPY.N and MSC) to
provide two concurrent data read paths. No writes
occur across the Y bus. This class of instructions dedi-
cates two W register pointers, W10 and W11, to always
address Y data space, independent of X data space,
whereas W8 and W9 always address X data space.
Note that during accumulator write back, the data
address space is considered a combination of X and Y
data spaces, so the write occurs across the X bus.
Consequently, the write can be to any address in the
entire data space.
The Y data space can only be used for the data
prefetch operation associated with the MAC class of
instructions. It also supports Modulo Addressing for
automated circular buffers. Of course, all other instruc-
tions can access the Y data address space through the
X data path as part of the composite linear space.
The boundary between the X and Y data spaces is
defined as shown in Figure 3-8 and Figure 3-8 and is
not user programmable. Should an EA point to data
outside its own assigned address space, or to a loca-
tion outside physical memory, an all zero word/byte will
be returned. For example, although Y address space is
visible by all non-MAC instructions using any address-
ing mode, an attempt by a MAC instruction to fetch data
from that space using W8 or W9 (X space pointers) will
return 0x0000.